Disk drive flexures are generally known and commercially available. Typical flexures transmit signals along disk drive suspensions. Flexures comprise traces that extend along the suspension to electrically connect disk drive control circuitry with electrical elements such as read/write transducers on the distal end of the suspensions. FIG. 1 shows a plan view of a flexure 1. The flexure 1 includes a proximal end 6 and a distal end 5. A trace array 4 extends along the flexure 1 from the proximal end 6 to the distal end 5. The trace array 4 can be one of several trace arrays, such as separate send and receive trace arrays. Traces of the trace array 4 carry signals that travel between the proximal end 6 and the distal end 5. The trace arrays 4 can electrically connect with transducers 7 or other electrical elements at a distal end 5 of the flexure 1. As shown, the distal end 5 of the flexure 1 includes a tongue 8 which can support the transducers 7. The transducers 7 can be configured to preform read and/or write functions with spinning disk media. The trace array 4 extends to a proximal end 6 of the flexure 1. The trace array 4 can electrically connect with disk drive control circuitry 20. The disk drive control circuitry 20 can include one or more processors configured to control the function of the hard disk drive, including reading and writing functions with the transducers 7 by sending and receiving signals along the trace array 4.
FIG. 2 shows a plan view of a section of the flexure 1 of FIG. 1. The flexure 1 comprises a base metal layer 2. The base metal layer 2 can extend from the proximal end 6 to the distal end 5 of the flexure 1. The base metal layer 2 can be formed from stainless steel, however other types of metal can alternatively be used, such as copper. The base metal layer 2 can be the major structural backbone of the flexure 1. For example, most or all of the structural rigidity of the flexure 1 can be provided by the base metal layer 2. The thickness of the base metal layer 2 can be between 10-20 micrometers, for example. The base layer 2 supports a dielectric layer 3. The dielectric layer 3 can comprise a first or bottom side that directly contacts the base metal layer 2. A preferred thickness (e.g., measured along the Z-axis) of the dielectric layer 3 is 10 micrometers, although a suitable thickness can range from 5-20 micrometers for various embodiments. The thickness of the base metal layer 2 can be between 10-20 micrometers, for example. The dielectric layer 3 can be attached to the base metal layer 2. The dielectric layer 3 can be formed from a polymer, such as polyimide.
FIG. 3 shows a plan view of the section of the flexure 1 of FIG. 2 but with insulating material, such as the dielectric layer 3, removed to show detail. FIG. 4 shows a cross sectional view of the trace array 4 along line AA of FIG. 2. The trace array 4 is located on the second or top side of the dielectric layer 3. The trace array 4 comprises a plurality of traces 11-14. The traces 11-14 can be located on the top surface of the dielectric layer 3 or may be partially or fully embedded in the dielectric layer 3. A covercoat 10 can be placed over the trace array 4. The traces 11-14 can be formed from copper, however other conductive metals or other conductive materials can additionally or alternatively be used. The trace array 4 includes a pair of outer traces 11, 14 and two inner traces 12, 13. The base metal layer 2 comprises a first lateral side 15 and a second lateral side 16 separated by window 41. The window 41 is defined laterally by a first lateral edge 18 and a second lateral edge 19 and proximally and distally by bridges 45. The bridges 45 comprise sections of the base metal layer 2 that span between the first and second lateral sides 15, 16.
The plurality of traces 11-14 of the array 4 can be interleaved. Interleaved trace arrays comprise traces of alternating polarities along a width of the flexure. Specifically, the disk drive control circuitry 20 (e.g., including routing by trace jumpers) can be configured to output signals to the plurality of traces 11-14 such that each trace is adjacent only to traces having the opposite polarity. Likewise, transducers 7 or other electrical elements electrically connected with the traces 11-14 can be configured to receive, and function using, the arrangement of alternating polarized signals corresponding to the interleaved array 4. Interleaving traces can reduce impedance and improve electrical performance characteristics of the trace array 4. U.S. Pat. No. 5,717,547 to Young and U.S. Pat. No. 8,300,363 to Arai et al. disclose flexures having interleaved trace arrays, each of which is incorporated herein by reference in its entirety and for all purposes.
The traces 11-14 can be interleaved such that trace 11 carries a first polarity (e.g., positive), trace 12 carries a second polarity (e.g., negative) opposite to the first polarity, trace 13 carries the first polarity, and trace 14 carries the second polarity. The polarities can reverse during data transmission and/or can be in a different arrangement. Respective electromagnetic fields are generated by current traveling down the traces 11-14. Specifically, an electromagnetic field radiates outward from each of the traces 11-14 (e.g., along the Y-axis). The window 41 is wide enough such that the electromagnetic fields generated by the traces 11-14 do not interact with the first lateral side 15 and the second lateral side 16 of the base metal layer 2. Specifically, the pair of outer traces 11, 14 are spaced far enough away from the first and second lateral sides 15, 16, respectively, such that the pair of outer traces 11, 14 do not capacitively couple with the first and second lateral sides 15, 16, respectively. Outer traces 11, 14 would commonly be separated from the first and second lateral side 15, 16 by 50 micrometers, respectively, to prevent electromagnetic interaction between the pair of outer traces 11, 14 and the first and second lateral sides 15, 16, respectively, which may otherwise lead to loss and degradation of the respective signals carried by the pair of outer traces 11, 14. The traces 11-14 are close enough to each other such that the fields interact with adjacent traces. For example, adjacent pairs of the traces 11-14 capacitively couple to each other when current passes though the traces. It is noted that each of the outer traces 11, 14 only capacitively couples to a respective one of the inner traces 12, 13, while each of the inner traces 12, 13 respectively couples to the other inner trace 12, 13 and one of the outer traces 11, 14. As such, inner traces 12, 13 have higher (e.g., double) the capacitive interaction as outer traces 11, 14. The difference in capacitive interaction complicates synchronous electromagnetic wave propagation in the traces 11-14, as further discussed herein.
The time delay of propagation of an electromagnetic wave in a trace is governed by following equation: Time Delay=1/(Square root of L*C), wherein L refers to the inductance of the trace and C refers to the capacitance of the trace. Being that the capacitance for the inner traces 12, 13 is double that of the outer trace 11, 14, electrometric waves travel faster on the outer traces 11, 14 than the inner traces 12, 13, resulting in an appreciable difference in time delay between the inner traces 12, 13 and the outer traces 11, 14. The difference in delay means that simultaneously sent signals (e.g., sent by disk drive control circuitry 20) will be out of phase or otherwise asynchronous with each other further down the trace, which may frustrate operations that depend on synchronous signal transmission between different traces. The rate of signal propagation in the inner traces 12, 13 can be increased by lowering the inductance of the inner traces 12, 13. Specifically, the inductance of the inner traces 12, 13 can be lowered by increasing the widths of the inner traces 12, 13 relative to the outer traces 11, 14. The inner traces 12, 13 can accordingly be made substantially wider than the outer trace 11, 14, as shown in FIGS. 3-4. The inner traces 12, 13 are commonly 3-4 times wider than the outer traces 11, 14. Such difference in width between the inner traces 12, 13 and the outer trace 11, 14 evens the rate of signal propagation in the traces 11-14 of the array 4 such that simultaneously sent signals are simultaneously received.
The consequence of increasing the widths of the inner traces 12, 13 is that the footprint of the trace array 4 is enlarged, which takes up precious space on the flexure 1, causes the flexure 1 to be large and crowd other components, and increases material costs. Various embodiments of the present disclosure concern techniques for addressing asynchronous signal transmission along traces.